Method of producing clad porous metal articles



June 30, 1964 H. A. KUCHEK 3,138,857

METHOD OF PRODUCING GLAD POROUS METAL ARTICLES Filed Oct. 9, 1961 INVENTOR.

If 4 Henry H. MIC/ 4 Z0 0 BY GBQQLQZL- H TTOQNfY United States Patent 3,138,857 METHOD OF PRODUCING CLAD POROUS METAL ARTICLES Henry A. Kuchek, Auburn, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Oct. 9, 1961, Ser. No. 143,623 2 Claims. (Cl. 29-423) This invention relates to a method of producing a clad, porous article of manufacture useful as a filter.

In the accompanying drawings, forming a part of this specification, and in which like numerals are employed to designate like parts throughout the same,

FIGURE 1 is a side view of a portion of the final product of this invention,

FIGURE 2 is a side view of a portion of the final product of this invention, partially in section,-

FIGURE 3 is a section view of an extrusion compact, from which the final product of FIGURES 1 and 2 is made, and,

FIGURE 4 is a magnified view of a small section of the salt-filled metal casting which forms the core of the extrusion compact shown in FIGURE 3.

The end product of the present invention illustrated in FIGURES l and 2, has a thin dense metal exterior surface 5 and a porous metal core 6. The article is formed with an axial bore constituting a conduit 7 running the length of the article. Through the exterior surface 5 of the article perforations or apertures 8 are provided to a depth sufficient only to expose the porous metal core 6. If a similar article of greater length is desired, the article may be threaded at the ends 9 to facilitate joining. Core metal 6 is of the nature of a metal sponge and has pores which are interconnected, longitudinally elongated, and of a generally uniform, relatively small diameter in the plane normal to the longitudinal axis of the article.

At the ends of the article, the core may be of solid non-porous metal bushings 10, and solid metal portions give support to threading 9 of the article, when threading is desired.

The article produced by the method of this invention is particularly useful as a rigid filter for separating solids from liquids, but the invention is not thus-limited. In use as a filter, the fluid material to be filtered is inserted in the bore 7 and by use of a bushing 10, the filtrate will be forced through the apertures 8. Of course, the reverse flow may also be used, i.e., the material to .be filtered forced through apertures 8 from the outside, and the filtrate recovered from the internal conduit 7.

Preparation of the article of thisinvention-is begun by casting a suitable metal or metal alloy, preferably aluminum or aluminum alloy'cont'aining at least 75 percent aluminum into a mold filled with a water soluble salt in granular form. Suitable sizes of ganular salt are those as small as will pass a 100 mesh screen and those as large as will allow sufficient metal to remain to result in a self-supporting article, sometimes as much as an inch in diameter or greater, depending on the size of the mold. While the shape of the salt 11 will preferably bejequiaxed, oblong or irregularly shaped pieces may be employed as shown in FIGURE 4. The salt must have a melting temperature higher than the temperature at which the metal or metal alloy is to be cast, must be insoluble in the liquid metal or metal alloy, must not be so strongly or rapidly corrosive in aqueous media toward the metal or metal alloy as to destroy the metal or metal alloy in the time required to leach the salt from the casting, and must not be reducible in aqueous media by the cast metal or metal alloy so as to leave an undesired metal residue in the porous core. Salts usable in the method of this invention are, for example, sodium chloride, potassium chloride, barium chloride, and the like which meet the requirements described above.

By proper selection of the salt to be employed in the casting step, keeping in mind the requisite properties described above, the practice of this invention may be extended to any extrudable metal or metal alloy, as for example, lead, magnesium, aluminum, tin, copper, and their alloys.

Prior to casting, the salt-filled mold is preheated to a temperature near the melting point of the metal or metal alloy, but without melting the salt. The molten metal is then poured into the hot salt-filled mold. Preheating the mold ensures a good penetration by the metal of the spaces between the salt grains and is particularly desirable if the salt grains are of a very small size.

The salt-filled metal casting 12 is allowed to cool and solidify and is then removed from the mold. As shown by FIGURE 4, the salt granules 11 are in contact with each other so that when they are removed, the voids left are interconnecting. A bore or conduit 13 of suitable size running the length of the longitudinal axis is necessary. Such a bore may be obtained at this stage by drilling, or its formation may be accomplished in the casting step by the provision of a suitable axially disposed core.

Referring to FIGURE 3, the metal-salt casting thus prepared is then placed in a jacket or sleeve 14 of a metal or metal alloy similar to that forming the porous metal, but in the normal dense and non-porous condition. The inner dimension of the jacket should be such as to provide a relatively close fit around the metal-salt casting, and have a wall thickness appropriate for the desired final thickness after extrusion. The metal-salt casting 12 forms the core of the article, and the jacket or sleeve 14 forms the solid outer surface of the article.

In order to give lateral support to the ends of the resulting article, a bushing 15 in each end of the sheathed porous metal is usually employed. This bushing 15 is fitted at the end of the salt-containing metal 12 and within the jacket 14. Bushings 15 may be solid or define a bore 16, the axis of which usually coincides with the axis of bore 13 defined by the salt-containing metal 12.

Salt-containing metal 12, encased by jacket 14, and optionally plugged by bushings 15 is hereinafter called an extrusion comp act.

In order to compress and tighten the jacket 14 around the porous metal, increase the overall length, decrease the overall diameter, elongate the pores and, if used,

" make the bushings 15 integral, the extrusion compact is extruded. Generally, an extrusion reduction ratio of at least 2 to l is accomplished, with ratios of 9 to 1 being preferred, and ratios as high as to 1 may be employed in some instances. During extrusion, provision is made to maintain the longitudinal bore 13 of the extrusion compact, as by extruding around a mandrel.

After extrusion, apertures of a depth sufiicient to expose the metal-salt core are drilled through the solid metal jacket of the article, but preferably are not drilled If desired, the ends of the article may be threaded at any time after extrusion.

During the extrusion step, the salt-containing pores are elongated in the direction of extrusion, which direction is parallel to the longitudinal axis of the article. Said salt-containing pores are also reduced in diameter in the plane normal to the longitudinal axis of the article. The salt is retained within the pores during extrusion to prevent collapse of the pore walls within the core.

Good uniformity of pore diameter is obtainable With this method. Said method has an advantage in that fairly coarse salt grains may be used in casting even though a fine pore diameter may be desired as a final product. If it were necessary to use salt grains of fine diameter, problems in casting might arise. The core metal would have diificulty in filling the voids uniformly, so that after leaching large gaps might appear in the porous structure. By proper selection of the size and shape of the water soluble salt grains, the extrusion reduction ratio, and the thickness of the cladding jacket, a large number of pore sizes and shapes may be obtained with a substantial degree of reproducibility.

The jacket is tightly bound'to the core by the pressures of the extrusion process so that an article of essentially unitary construction is finally obtained.

The following example is set forth to illustrate, but not to limit, this invention.

Example A cylindrical mold having a diameter of 3 inches and a depth of 8 inches was prepared by filling it with sodium chloride granules of an 8-12 mesh size, U.S. sieve series. The sodium chloride containing mold was preheated to about 700 C. An aluminum alloy having the nominal composition of percent silicon, balance aluminum was cast at a temperature of about 760 C. into the mold.

After solidification, the metal-salt cylinder was re moved from the mold and machined to a 2 /2 inch diameter. A inch diameter bore was drilled longitudinally through the center of the cylinder and the cylinder was then fitted into a 2 /2 inch diameter metal sleeve having a 7 inch wall thickness, and having a nominal composition of 0.4 percent silicon, 0.7 percent magnesium, and the balance aluminum.

Pure aluminum bushings 15 were inserted into each end of the sleeve to form an extrusion compact. The extrusion compact was then preheated to about 425 C., placed in a 500 ton extrusion press with a inch mandrel and extruded through a conical die having a face set 60 from the line of extrusion and a 1 inch opening. The extrusion reduction ratio was about 9:1 and the extrusion speed was about 3 feet per minute. The temperature of the extrude leaving the die was about 425 C.

A series of apertures 8, having a diameter of inch and a depth of /8 inch, were provided by drilling on half inch centers on each of equally spaced longitudinal markings the length of the cladding jacket. .The ends of the extrude were threaded 9 for a pipe fitting. One end of the extrude was sealed with a pipe cap. Water at 60 p.s.i. was forced through the extrude from the outer end to leach the salt 11 from the porous metal.

An examination of the thus-prepared article showed that the cladding jacket had a thickness of about inch, there was a good bond between the cladding jacket and the porous metal, and the pores were elongated, interconnecting, and of uniform small diameter.

When the article produced by the metal of this invention is used as a fluid filter, suspended solids are removed from the fluid to a high degree of efiiciency. After a period of use, the filter may be cleaned or rejuvenated by simply flushing, suitably in the reverse direction of flow, for a short time.

The article produced by the method of this invention has good structural characteristics. It is self-supporting without the basic weakness common to unclad metal sponge of like dimensions. Further, the porous core is protected from damage which may occur in handling, shipping, etc.

Various modifications may be made in the present invention without departing from the spirit or scope thereof, and it is to be understood that I limit myself only as defined in the appended claims.

I claim:

1. The method of producing a clad, porous, metal article which comprises casting a metal into a mold filled with water soluble salt granules which have a melting point above the temperature at which the metal is cast, removing the salt-metal casting from the mold after solidification, providing an axial bore the length of the casting, inserting the casting into a dense metal jacket, subjecting the assembly thus-formed to an extrusion process, providing apertures in the jacket to a depth sufiicient to expose the salt-metal core, and forcing Water through the salt laden core to leach the water soluble salt from the porous core of the article.

2. The method of producing a clad, porous, metal article which comprises casting a metal of the class of aluminum and aluminum alloys into an elongated mold of regular cross section filled with water soluble salt granules which have a melting point above the tempera ture at which the metal is cast, removing the salt-metal casting from the mold after solidification, providing an axial bore the length of the casting, inserting the bored casting into a dense metal jacket of a metal of the class of aluminum and aluminum alloys, inserting at either end of the jacket, bushings of a metal of the class of aluminum and aluminum alloys which are bored coaxially with the longitudinal axis of the casting, subjecting the assembly thus-formed to an extrusion process, providing apertures in the jacket to a depth sufiicient to expose the salt-metal core, and forcing Water through the salt laden core to leach the water soluble salt from the porous core.

References Cited in the file of this patent UNITED STATES PATENTS 872,621 Gray Dec. 3, 1907 2,628,417 Peyches Feb. 17, 1953 2,770,367 Donato Nov. 13, 1956 2,983,597 Elliott May 9, 1961 2,986,810 Bricks June 6, 1961 3,006,044 Mayer Oct. 31, 1961 3,070,233 Welch Dec. 25, 1962 FOREIGN PATENTS 468,790 Italy Dec. 31, 1952 

1. THE METHOD OF PRODUCING A CLAD, POROUS, METAL ARTICLE WHICH COMPRISES CASTING A METAL INTO A MOLD FILLED WITH WATER SOLUBLE SALT GRANULES WHICH HAVE A MELTING POINT ABOVE THE TEMPERATURE AT WHICH THE METAL IS CAST, REMOVING THE SALT-METAL CASTING FROM THE MOLD AFTER SOLIDIFICATION, PROVIDING AN AXIAL BORE THE LENGTH OF THE CASTING, INSERTING THE CASTING INTO A DENSE METAL JACKET, SUBJECTING THE ASSEMBLY THUS-FORMED TO AN EXTRUSION PROCESS, PROVIDING APERTURES IN THE JACKET TO A DEPTH SUFFICIENT TO EXPOSE THE SALT-METAL CORE, AND FORCING WATER THROUGH THE SALT LADEN CORE TO LEACH THE WATER SOLUBLE SALT FROM THE POROUS CORE OF THE ARTICLE. 